Various kinds of electronic devices have spread, and a wide variety of products have been shipped to the market. In recent years, portable electronic devices such as cellular phones and digital video cameras have widely spread. Further, electric propulsion moving vehicles that are powered by electric power, such as electric cars, appear on the market as products.
Cellular phones, digital video cameras, and electric propulsion moving vehicles include batteries that are energy storage means. The batteries are charged while being in direct contact with home AC sources that are power transmission means in many cases. In a structure without a battery or a structure where electric power stored in a battery is not used, electric power is directly transmitted to an electronic device from a home AC source through a wiring or the like so that the electronic device operates.
On the other hand, methods by which batteries are charged wirelessly or electric power is transmitted to loads wirelessly have been researched and developed. Typical methods are an electromagnetic coupling method (also referred to as an electromagnetic induction method), a radio wave method (also referred to as a microwave method), and a resonance method. As electronic devices such as small household electrical appliances, devices utilizing the electromagnetic coupling method have spread.
Resonant wireless power transmission systems have been developed in order to increase the efficiency of electric power transmission as disclosed in References 1 to 3.